The GI tract wall is composed of four main layers: the mucosa, submucosa, muscularis externa, and serosa or adventitia.
- Mucosa: This innermost layer includes the epithelium, lamina propria, and muscularis mucosae. The epithelium varies from stratified squamous in the esophagus to simple columnar in the intestines, reflecting their different functions. - Submucosa: A dense connective tissue layer containing blood vessels, lymphatics, and the submucosal plexus (Meissner's plexus). - Muscularis externa: Composed of an inner circular and an outer longitudinal layer of smooth muscle, controlled by the myenteric plexus (Auerbach's plexus). - Serosa/Adventitia: The outermost layer, serosa is present in intraperitoneal organs while adventitia is found in retroperitoneal structures.
